The present invention relates to a thread wound golf ball. More particularly, it relates to a thread wound golf ball having long flight distance, while maintaining the characteristics peculiar to the conventional thread wound golf ball, i.e. good shot feel and excellent spin performance.
Thread wound golf balls consist of a solid or liquid center, a thread wound layer formed on the center and a cover of ionomer resin or balata etc. covering on the thread wound layer. The thread wound golf ball, when compared with the solid golf ball such as two-piece golf ball, generally has better shot feel at the time of hitting and better controllability at approach shot because of excellent spin performance. The thread wound golf ball is generally approved of or employed by high level golfers, especially professional golfers, who regard the characteristics as most important. However, the thread wound golf ball is inferior in flight distance to the solid golf ball, because the thread wound golf ball has large spin amount and small launch angle. Therefore the thread wound golf ball having sufficient flight distance, while maintaining the advantage of good shot feel and excellent controllability, is required.
In order to solve the problem, a thread wound golf ball comprising a solid center, thread rubber layer and cover, which has further long flight distance while maintaining excellent shot feel and controllability by adjusting material and physical properties of the solid center, such as a diameter, hardness, hardness distribution and deformation amount; and a hardness of the cover; to suitable ranges, has been proposed (Japanese Patent Kokai Publication Nos. 271537/1997, 271539/1997, 201881/1998, 299935/1999 and the like).
In Japanese Patent Kokai publication No. 271537/1997, a thread wound golf ball, of which the solid center has a diameter of 30 to 38 mm, a surface hardness in JIS-C hardness of 40 to 80 and a hardness difference from the central point to the surface in JIS-C hardness of not more than 5, and the cover is formed from a base resin comprising ionomer resin as a main component and has a flexural modulus of 300 to 600 MPa and a Shore D hardness of 60 to 80, is described.
In Japanese Patent Kokai publication No. 271539/1997, a thread wound golf ball, of which the solid center has a diameter of 35 to 38 mm and a deformation amount of 3.5 to 6.0 mm when applying a load of 130 kg (initial load of 10 kg), a deformation amount difference from that of the solid center to that of the golf ball is within the range of 0.5 to 3 mm, and the cover has a Shore D hardness of 65 to 75, is described. In the golf ball, the spin amount of is restrained, and the flight distance is increased.
In Japanese Patent Kokai publication No. 201881/1998, a thread wound golf ball, of which the solid center has a diameter of 30 to 38 mm, a surface hardness in JIS-C hardness of 40 to 90, a hardness difference from the central point to the surface in JIS-C hardness of not more than 5 and a deformation amount of 0.5 to 2.5 mm when applying a load of 30 kg (initial load of 10 kg), and the cover is formed from a base resin comprising ionomer resin as a main component and has a flexural modulus of 50 to 300 MPa and a Shore D hardness of not less than 40 to less than 60, is described. In the golf ball, it is easy to put spin thereon when hit by an iron club.
In Japanese Patent Kokai publication No. 299935/1999, a thread wound golf ball, of which the cover has a two-layer structure composed of an inner cover and an outer cover having higher hardness than the inner cover, the outer cover has a Shore D hardness of 55 to 65, a total thickness of the inner cover and outer cover is within the range of 2.0 to 5.0 mm, the thread rubber layer has a thickness of 1.0 to 2.5 mm, and the solid center has a diameter of 29 to 37 mm. In the both golf ball, the scuff resistance when hit by an iron club is excellent and the spin performance, shot feel and flight distance when hit by a driver are improved.
However, in order to improve the flight distance in the conventional thread wound golf ball with solid center, it has been proposed to soften the solid center to restrain the spin amount, or to increase the diameter of the solid center and heighten the cover hardness, as described above. The flight distance is improved, but the spin performance is poor. When the thread wound golf ball is prepared by using soft center, while maintaining the characteristics peculiar to the thread wound golf ball, i.e. excellent spin performance by using soft cover, the hardness of the golf ball is low, and the rebound characteristics are degraded. In order to restrain the deterioration of the rebound characteristics, it is required to increase an extension of a thread rubber when winding the thread rubber around the solid center, and there is problem that the thread rubber easily breaks at the process of winding it.
Therefore, the thread wound golf ball, which has sufficient flight distance as same as solid golf balls, while maintaining the advantage of good shot feel and excellent controllability in the thread wound golf balls, has not been obtained. The thread wound golf ball having further excellent shot feel and controllability and long flight distance is required.
A main object of the present invention is to provide a thread wound golf ball, of which the flight distance is improved, while maintaining good shot feel and excellent spin performance.
According to the present invention, the object described above has been accomplished in a thread wound golf ball comprising a solid center by adjusting a diameter of the solid center, a thickness of the thread rubber layer and a thickness and hardness of the cover to a specified range, thereby providing a thread wound golf ball, of which the flight distance is improved as long as possible, while maintaining the characteristics peculiar to the thread wound golf ball, i.e. good shot feel and spin performance.
This object as well as other objects and advantages of the present invention will become apparent to those skilled in the art from the following description with reference to the accompanying drawings.